The applicant claims and requests a foreign priority, through the Paris Convention for the Protection of Industry Property, based on a patent application filed in the Republic of Korea (South Korea) with the filing date of Jul. 30, 2001, with the application number 2001-0046024, by the applicant. (See the Attached
The present invention relates to a piston assembly for an internal combustion engine. More particularly, the invention relates to a piston assembly for an internal combustion engine which prevents air from an air source for an internal combustion engine like an air cleaner or a turbo charger from leaking into the inside of the piston assembly and prevents lubrication oil leak from a crankcase into a combustion chamber of the engine thereby reducing lubrication oil loss and incomplete combustion.
An internal combustion engine comprises one or more cylinders and pistons, which move reciprocally in the cylinders. For example, as shown in. FIG. 1, a two-cycle internal combustion engine includes a piston assembly 10, and a cylinder liner 12, which surround the piston assembly 10, and fits into a cylinder (not shown). In the middle part of the cylinder and between the cylinder liner 12, is formed an air intake port 14.
The piston assembly 10 includes a piston 16, a plurality of grooves 18 formed at the outer periphery of the upper part of the piston 16, compression rings 17 inserted into the grooves 18 to keep sealing between the piston 16 and the cylinder liner 12. The Piston assembly 10 has also two grooves 20, 22 formed at the outer periphery of the lower part of the piston 16, an oil ring 24 inserted into the groove 22 and another oil ring, or an oil scraper ring 26 inserted into the groove 20, which is positioned above the groove 22.
The oil ring 24 collects lubrication oil and returns it to the crankcase of the engine. The oil-scraping ring 26 scrapes down lubrication oil spread on the cylinder liner 12. The entire outer periphery or a portion of the periphery of the oil scraping ring 26 contacts the cylinder liner 12, and adjusts the thickness of the lubrication oil film by scraping down excess oil. An oil passage 28 is formed between the grooves 20, 22 to communicate the inside of the piston 16 and the gap between the outer cylindrical wall of the piston 16 and the inner wall of the cylinder liner 12.
FIGS. 2 through 4 show the oil scraper ring 26. The oil scraper ring 26 has an upper rail 30 and a lower rail 32. Diameters of the rails are the same. A plurality of evenly spaced scallops 34 is formed on the lower rail 32. The scallops 34 pass the oil collected by the upper rail 30 to the crankcase via the oil passage 28.
At down stroke of the piston""s reciprocal movement, air pressure builds up within the space confined by the inside of the piston, the cylinder, and the crankcase. The pressure forces some oil from the inside of the piston 16 to be leaked into the gap between the cylinder liner 12 or the inner wall of the cylinder and the piston 16. The leaked oil eventually reaches the air intake port 14 and flows into the combustion chamber causing incomplete combustion.
The cause of this phenomenon is explained referring to FIG. 5. While a semi-vacuum state is formed in the space below the piston at upstroke of the piston""s reciprocal movement, at down stroke, a portion of air flowing in via the air intake port 14 passes through a gap between the cylinder liner 12 and the oil scraper ring 26, or through a gap between the oil scraper ring 26 and the groove 20. The leaked air flows into the inside of the piston 16 via the scallops 34 and the oil passage 28. As the piston 16 moves down further, the air in the space below the piston 16 is compressed to increase the air pressure within the space. The increased pressure causes a reverse air flow via the path explained above. This reverse flow forces oil spread on the cylinder liner 12 or on the outer wall of the piston 16 to be sprayed onto the portion of the cylinder liner 12 near the air intake port 14. The sprayed oil is flowed into the combustion chamber together with the intake air and burned together with the fuel.
Since the ignition point of oil is higher than that of fuel, such combustion of the mixture of oil and fuel causes incomplete combustion, reduction of combustion efficiency, excessive consumption of fuel, and exhausting smoke. Another problem is that the pressure buildup hinders down stroke movement of the piston, and causes engine efficiency drop or noise. Still another problem is excessive consumption of lubrication oil due to the combustion of the leaked oil.
Such problems are inherent to the construction of an oil ring, a cylinder, and a cylinder liner of prior art. The portion of the cylinder around the air intake port is machined to have an increasing size considering thermal expansion. However, since the diameters of the rails of the oil-scraping ring are the same, when the piston is at the top dead point or at down stroke, the lower rail 32 contacts the cylinder liner but the upper rail 30 does not contact the cylinder liner. Therefore, a gap is formed between the cylinder liner and the oil-scraping ring, providing a leakage path.
Accordingly, there has been a demand for an improved sealing mechanism between an oil ring of a piston assembly and a cylinder liner of an internal combustion engine.
The present invention is contrived to overcome the conventional disadvantages. Therefore, an object of the invention is to provide an enhanced sealing mechanism for a piston assembly for an internal combustion engine.
Another object of the invention is to prevent air leak into the inside of the piston assembly.
Still another object of the invention is to prevent oil leak into a combustion chamber of the engine.
Still another object of the invention is to prevent excessive pressure buildup in a crankcase of the engine.
Still another object of the invention is to prevent formation of gaps around the oil ring in its assembled state.
To achieve the above-described objects, in accordance with an embodiment thereof, the invention provides a piston assembly for an internal combustion engine comprising a piston that has a shape of a cylinder and has an outer cylindrical wall and a top portion on one end of the cylinder; an oil ring that is pressed against a cylinder liner of the internal combustion engine; and a circular groove that is formed in the outer cylindrical wall of the piston and holds the oil ring. The groove has an upper wall, a sidewalk, and a lower wall and the upper wall is positioned toward the too portion of the piston. The piston assembly further includes a circular recess that is formed in the upper wall of the groove and a sealing member that is inserted into the recess and contacts the oil ring.
The sealing member may be an elastic member and in the assembled state within the circular groove, the sealing member is compressed to provide sealing between the groove and the oil ring. Preferably, the sealing member is an O-ring.
In accordance with another embodiment thereof, the invention provides a piston assembly for an internal combustion engine comprising a piston that has a shape of a cylinder and has an outer cylindrical wall and a top portion on one end of the cylinder, an oil ring that has an upper projection and a lower projection that are formed on an outer periphery of the oil ring, a circular groove that is formed in the outer cylindrical wall of the piston and holds the oil ring.
The upper projection of the oil ring is positioned toward the top portion of the piston. Both of the projections of the oil ring have tapered edges, and the outer diameter of the upper projection is greater than the outer diameter of the lower projection.
The groove has an upper wall, a sidewall, and a lower wall and the upper wall is positioned toward the top portion of the piston. The piston assembly further includes a circular recess that is formed in the upper wall of the groove and a sealing member that is inserted into the recess and contacts the oil ring.
Preferably, the difference between the outer diameters of the upper projection and the lower projection is from about 0.2 cm to about 0.6 cm. More preferably, the difference is about 0.4 cm.
Preferably, the thickness of the edge of the upper projection is greater than the thickness of the edge of the lower projection.
In accordance with another embodiment thereof, the invention provides a piston assembly for an internal combustion engine comprising a piston that has a shape of a cylinder and has an outer cylindrical wall and a top portion on one end of the cylinder, an oil ring, and a circular groove that is formed in the outer cylindrical wall of the piston and holds the oil ring.
The oil ring has an outer periphery, an inner periphery, a top portion, a bottom portion, a recess that is formed along the inner periphery, an upper edge that connects the top portion and the recess, a lower edge that connects the bottom portion and the recess, and an elastic member that is inserted into to the recess of the oil ring and presses the oil ring against a cylinder liner of the internal combustion engine. The radii of the upper and lower edges of the oil ring are less than the inner radius of the elastic member.
Preferably, the difference between the radii of the upper and lower edges of the oil ring and the inner radius of the elastic member of the oil ring is about 0.5 mm.
The advantages of the present invention are numerous in that: (1) oil leak or air leak through a gap between the oil ring and the groove holding the oil ring is prevented by the sealing member provided at the recess in the groove""s wall; (2) the sealing between the oil ring and the groove is further enhanced with the extended upper and lower edges of the oil ring; and (3) oil leak or air leak through a gap between the piston assembly and the cylinder liner is prevented by the upper and lower projections of the oil ring wherein the diameter of the upper projection is bigger than that of the lower projection and the edge of the upper projection is thicker than the edge of the lower projection.